In an attempt to minimize the redesigning of standard automotive transmissions so as to incorporate a reliable speed sensor, the present inventor has developed a novel transmission speed sensor which requires little or no extra space within the transmission housing.
While there have been significant mechanical improvements in engine, suspension and drive train technology, the past decade can be characterized by an electronic revolution in the automotive industry.
Electronic control units (ECU) amass information from sensors and command the action of many vital functions in today's automobile. There are four major categories in which electronic controls have made substantial inroads: (1) engine, (2) transmission, (3) suspension, and (4) anti-lock braking/traction control. In all of these cases the signals of the rotational motion or position change of components are fed to the ECU, which compares them to a calculated or mapped value ideal for the operational conditions. The ECU then initiates changes in the controlled function in order to minimize deviation from ideal conditions. For this scheme to work effectively, high reliability, good resolution and economic sensor systems are required.
In order to sense motion/position in an automobile, there are four distinct systems that have evolved: (1) passive or variable reluctance sensors, (2) active sensors, such as Hall-effect sensors, (3) optical sensors, and (4) accelerometers. Variable reluctance sensors have been used predominantly in anti-lock braking systems (ABS) for wheel speed sensing and in automatic transmission output speed sensing. Hall-effect sensors have been used mostly in ignition systems, while optical sensors and accelerators are used in suspension control systems.
This invention relates primarily to sensors used to detect the output speed of automobile transmissions. Currently, variable reluctance sensors are used to sense transmission output speed. These sensors typically measure the change in magnetic field strength as a ferromagnetic exciter ring or toothed wheel passes a detector. That is, the moving teeth of the exciter ring change the magnetic flux in the vicinity of a variable reluctance detector, i.e., a coil and magnet, and pulses of electrical current are induced. The output from the coil is sinusoidal, with an frequency proportional to the speed of the exciter ring. The frequency of the detector signal is used to calculate the rotational speed of the transmission.
U.S. Pat. No. 3,716,788 to Nishida, describes a conventional variable reluctance sensor which is added to a wheel bearing assembly to measure axle speed. A toothed rotor is formed on a revolvable inner bearing ring opposite a toothed stator fixed to a stationary outer bearing ring. The bearing outer ring also supports the magnetic coil pickup or detector which produces a voltage in accordance with the changes in magnetic flux induced by alignment of the rotor and stator teeth during rotation. The frequency of the alternating current produced is in proportion to the rotational speed of the axle.
A similar type speed sensor is disclosed in U.S. Pat. No. 3,826,933 to Anselmino. This speed sensor has a magnetic pickup coil or detector secured to the stationary ring of a bearing while a wheel having ferromagnetic teeth is secured to the rotatable ring of the roller bearing.
The problem associated with using variable reluctance sensors to measure the output speed of a transmission involves the current practice of providing a separate exciter ring or toothed wheel with multiple teeth positioned on the transmission output shaft. These variable reluctance sensors require the addition of a separate exciter ring to the transmission which takes up precious space, increases product cost and increases the overall weight of the transmission. Typically, the space required for conventional variable reluctance sensor systems is not available unless the sensor is specifically designed into an entirely new transmission. For example, in a typical rear wheel driven passenger car, the adaptation of a sensor within a transmission must take into consideration the added space for an exciter ring at the expense of some other important design considerations, such as overall size.
Another problem associated with variable reluctance sensors using separate exciter rings is that movement by the exciter ring may cause inaccurate magnetic field measurements.
Any sensor that minimizes system mechanical redesign, meets performance requirements, reliability and cost requirements, is considered extremely desirable by automobile designers. Therefore, the present inventor undertook the task of developing a transmission speed sensor which requires little or no extra space in the transmission, is highly reliable, and is cost effective.
The present invention involves the application of a redesigned integral thrust bearing assembly with a variable reluctance sensor and a thrust bearing assembly with a Hall-effect sensor. Although thrust bearing assemblies have been known to utilize Hall-effect and variable reluctance sensors as evidenced in U.S. Pat. No. 4,875,785 to Santos et al., the present inventor has uniquely redesigned the thrust bearing assembly of an automobile transmission to incorporate either a Hall-effect or integral variable reluctance sensor.
The present invention is applicable to any power transmission device which uses thrust bearings. This includes transfer cases for four wheel drive capability, differentials, torque convertors and power take-off units. The present invention is also applicable to input shafts and intermediate shafts within any power transmission device.
Additional advantages of the present invention shall become apparent as described below.